Choline base (.beta.-hydroxyethyl trimethylammonium hydroxide) is a well-known organic base suitable for a variety of uses. For example, aqueous solutions of choline base are useful in connection with electronic applications such as positive photoresist developing agents, as anisotropic etching agents, and as washing agents for silicon wafers. Use in the electronics area requires that there be no residue following the normal post bake period because even traces of impurities such as alkali metals would interfere in the operation of the electronic circuits. Accordingly, impurity specifications for choline base to be used in the electronics industry are very strict. Typically such specifications are, based upon contained choline base, .ltoreq.10000 ppm Cl, Br, I, or carbonate and .ltoreq.15 ppm each of Li, Na, and K. It is understood, however, that it is advantageous to the electronics fabricator to employ choline base in which the above mentioned impurities approach zero.
Choline base has been produced by various techniques in the past such as illustrated in U.S. Pat. No. 2,774,759. In addition it is known to manufacture quaternary ammonium hydroxides by use of electrochemical processes. Typical U.S. Pat. Nos. involving such processes include 2,363,386; 2,363,387; 3,402,115; and 3,523,068. However, none of these patents specifically mention choline base. It is also known that sulfite stabilizing agents are useful to retard color darkening when added to developing solutions such as trialkylmonoalkanolammonium hydroxide. This function of sulfites is illustrated in U.S. Pat. No. 4,294,911 and in an article by J. R. Guild which appeared in Res. Disc., 186, pages 575-576, (1979).